Sheet metal joining processes are widely used in many industries, such as the aerospace and automotive industries. Among these processes, resistance spot welding is the most common procedure used to join metal sheets because it has high process speed and is easily adopted in mass production lines; however, seam welding, weld bonding, adhesive joining, soldering, and brazing are gaining more widespread acceptance. The quality control of such joining processes is an important issue to manufacturers.
The quality of such joints is affected by the joining process itself and the design of the joint. Many factors have to be taken into account, such as metallurgic reactions, thermal behaviors, chemical composition, condition of the base metal, welding and bonding conditions, and the welding and bonding equipment. Furthermore, the intricate relationship between these factors makes it more difficult to control the quality of the joint, and difficult to inspect the joint in a nondestructive manner.
Acoustic methods are commonly used nondestructive testing methods that have been used for various inspection applications. Unlike other nondestructive testing methods, the acoustic method provides both surface and internal information. Moreover, the acoustic method allows deeper penetration into specimens and higher sensitivity to small discontinuities. Acoustic methods, however, are not flawless. The most significant limitations include the requirement of skillful operators for operating the device and analyzing the acoustic information, as well as the very subjective nature of identifying a stuck, or cold, weld or inadequate bond, such as a kissing bond.
The field of ultrasonic nondestructive evaluation (NDE) inspection techniques has needed a reliable way of identifying poor quality joints in a manner that eliminates the need for a skilled operator while still providing improved reliability by eliminating the subjective nature of prior techniques. While some of the prior art devices have attempted to improve the state of the art, none has achieved the unique and novel configurations and capabilities of the present invention. With these capabilities taken into consideration, the instant invention addresses many of the shortcomings of the prior art and offers significant benefits heretofore unavailable.